In the global context, it is imperative for the construction mode of the construction industry to develop toward prefabricated mode. The continuous improvement in the construction technology of the prefabricated concrete buildings offers technical foundations for improving the performance of the precast fabricated structure and realizing the housing industry. A prefabricated concrete structure is a concrete structure assembled by precast concrete components through a reliable connection, and then the prefabricated concrete structure, cast-in-place concrete, and cement-based grouting material form an entirety which is exactly the assembled monolithic concrete structure. The core and difficult point of the prefabricated construction is to ensure the connection quality of steel bars. It is hard to ensure the coaxial connection of the to-be-connceted steel bars with the available techniques and skills. At present, the connection of the precast components is commonly realized by pouring non-shrink or small-expansion cement-based grouting material to half-grout or full-grout sleeve. However, it is difficult to ensure that the sleeve is fully filled with grouting materials and the grout has low porosity with the available construction technology. Moreover, there are no effective technical means to detect the percentage of compaction of grouting in the specific engineering construction. Therefore, the development and use of prefabricated buildings in areas with high requirements of seismic fortification are restricted. In order to realize the universality of the prefabricated construction technology, it is necessary to targetedly improve the connection structure and construction skill regarding the above problems.
Since the full-grout sleeve has large geometric size, large grouting work load, high construction difficulty, and the range of steel bar critical region around the connection node is wide, the half-grout sleeve is commonly used in engineering at present. The widely used half-grout sleeve is an iron casting component. One end of the half-grout sleeve is directly connected to the steel bar bolt, and the other end is directly connected by the grout. In the construction site, the ribs on the steel bar must be fully removed. One end of the steel bar is subjected to cold-rolling to form screw thread, and then connected to the half-grout sleeve through thread connection. Such connection has the following drawbacks: (1) The procedure of processing thread on site is complex and the standard of quality is hard to be controlled. (2) When performing the thread connection on the construction site, the torque wrench must be used, which increases the operative difficulty. (3) The length of steel bar inserted into grout sleeve and the quality of thread connection should be controlled to satisfy the requirements of national standards, so it is extremely difficult to achieve a high qualification ratio. (4) According to the disclosure of prior art, for the half-grout connection structure, the number of ribs of the non-grout connection section and the side wall of the grout sleeve are increased to improve the strength of the connection part of the prefabricated concrete components, so that the sleeve wall is thick and heavy.
In addition, there are also half-grout sleeves, which are made by performing mechanical cutting process on steel rod or rolling process on finished seamless steel tube. For mechanical cutting process of steel rod, the cutting workload is large and the cost of processing is high, and the drawbacks of the above-mentioned connection construction of steel bar still exist. For example, a novel joint for cement grout rebar disclosed in Chinese patent CN102116075A is essentially a half-grout sleeve made by milling rolled profile steel.
Currently, the connection of the prefabricated concrete components mainly used is grout sleeve connection. The core and difficult point is to ensure the quality of steel bar connection of the prefabricated concrete components. It is difficult to ensure the coaxial connection of the steel bars in the grout sleeve with the available techniques and skills. According to statistics, in the engineering practice, the accurate connecting rate between the sleeve and the steel bar extending outward is about 20%, which is caused by the following reasons. (1) It is hard to insert the steel bars extending outward from the end of the same component into the corresponding sleeve, as a result the installation of the components is hard. (2) The steel bar of the grout connection section closely contacts the inner wall of the sleeve when being inserted into the grout sleeve, so in the subsequent step of grouting the steel bar of the grout connection section cannot be completely wrapped around by the grout. As a result, the connection strength of the sleeve greatly reduces, and the load transferring ability at the connection part of the components is seriously degraded.
In addition, after the assembly of the last prefabricated concrete structure is completed, the exposed steel bars may bend or get horizontally displaced due to grouting or other external reasons, so the grout sleeve of the next prefabricated concrete structure is not in the same vertical direction of the former one. Therefore, before assembly, steel bars need to be straightened and the horizontal position should be adjusted. In the prior art, such process is generally carried out by manually striking with the wrench or bending with the plier, so it is noisy while low accuracy is obtained.